The invention relates to a piston pump, preferably executed as a bore wash pump, comprised of a back-and-forth moving piston in a cylinder and an integrated filter piston.
Pseudo-continuously operating piston pumps take in fluid in an initial operating stroke through a spring-biased intake valve into a pump chamber and then compress it in a second operating stroke and finally discharge it through an discharge valve.
Wash bore pumps take up bore wash water heavily burdened with solids at low pressure and provide, at separate discharges, both filtered bore wash water and concentrated solid-containing bore wash water at higher pressures. Because of the heavy solid concentration in bore wash water, regular back flushing of the filter is required to prevent permanent clogging of the filter.
According to U.S. Pat. No. 5,534,145, a piston pump includes a filter equipped to purify fluids that is immovably arranged inside the cylinder. No back flushing is possible in such an arrangement.
According to U.S. Pat. No. 3,915,071, a multiple cascade, reciprocating piston, of a piston pump, is designed as a filter piston comprised of porous material that simultaneously compresses and purifies. This type of construction is not suitable for heavily contaminated fluids. Furthermore, back flushing of the filter is not possible with such a construction.
The object of the present invention is to provide a filtering piston pump for fluids heavily burdened with solids.
This object is achieved, in accordance with the invention, by a piston pump, wherein a sealing reciprocating piston, in a cylinder, has an automatically closing intake valve to a pump chamber with a spring-biased pre-stressed, axially limited, sealing, moving pre-mounted filter piston. The filter piston together with the piston form an automatically closing discharge valve.
In an initial operating stroke, the piston increases the pump chamber by its axial up stroke, whereby a negative pressure is created with the discharge valve closed. Such an arrangement, consequently allows the solid-burdened fluid to flow into the pump chamber through the opened intake valve. In a second operating stroke, the pump chamber is reduced by the down stroke movement and the solid-burdened fluid is compressed, whereby the filter piston arranged upstream is moved toward the piston against the bias and opens the discharge valve. Such an arrangement allows the purified fluid that has been filtered through the filter piston and compressed by the piston to flow out. The fluid with concentrated solids accumulates in the pump chamber. Consequently, the pump function is combined with the filter function in a limited space.
Advantageously, the piston pump comprises an automatically closing concentrate discharge valve to the pump chamber, which releases the fluid containing the concentrated solids at an overpressure in the pump chamber created by the separation by the filter. Consequently, the piston pump can be used to purify even fluids with a heavy burden of solids and fluids that vary markedly in their concentration of solids.
The automatically closing discharge valve is additionally advantageously stroke dependent closing at the terminal side, whereby the discharge valve is closed shortly before the lower dead center of the down stroke by a filter piston abutting the cylinder. Such an arrangement causes a back flow of the purified fluids through the piston filter into the pump chamber. As a result, an overpressure is created in the pump chamber, which, in a third operating stroke, expels the fluid containing the concentrated solids through the concentrate discharge valve. The piston pump is quasi-continuously self-cleaning.
The terminal stroke dependent closing discharge valve is advantageously spring-biased with an discharge valve spring via a tension bar. Consequently, such an arrangement is inexpensive to construct.
Other features and advantages of the present invention will become more apparent from the following description of the invention which refers to the accompanying drawings.